Among the very familiar shells are the land snails (Fig. 109), common in every garden and raised and sold in France and Italy as table delicacies. Closely allied to them are the slugs, which bear upon their backs, beneath the skin, a delicate, scale-like shell. On the island of San Clemente, fifty miles off the coast of California, I found an extensive sandy plain which was so thickly strewn with the white, bleached snail shells that I could hardly step without crushing several. The verdure had died, and the snails were doubtless killed by the direct rays of the sun.
These interesting animals are called pulmonates because they breathe air directly.
The slugs (Fig. 110) have many peculiar characteristics. If the long tentacles on the short eye stalk are destroyed, the snail will reproduce them. In winter the snails descend into the ground, or hide themselves away, literally sealing themselves in their shells by closing the door firmly, and there hibernate until spring, neither eating nor drinking, and hardly breathing during this time; if placed in a cold storage box, they will remain several years in this state.
Fig. 109.—A snail crawling.
Fig. 110.—Slugs and snails.
Some of the snails of Africa are six inches across, and the eggs are an inch in length. Semper found a little snail in the Philippines, which when caught by the foot or "tail" throws it off as a lizard jerks off its tail. This is not a great hardship, as the tail is soon renewed. In a collection of shells which came from France some years ago I found several snails of different colors which were joined one to the other. The collector had cut the top from an empty brown snail and placed a living snail with a yellow shell upon it, tying the two together. The snail, supposing that its shell had been broken, immediately began to repair the wound, and closed up the breach with its shell-secreting mantle, so that the two shells became one.